The display of the various timepiece functions is often complex in mechanical timepieces which include complications. The spatial distribution of the outputs of these complication mechanisms often makes direct display by hands or discs inconvenient, and requires the use of intermediate wheels, which further complicate the timepiece, make it more expensive and increase its thickness.
Other functions require providing the user with rapid and approximate information, this is especially true of power reserve displays, which indicate to the user when recharging is desirable.
Every display consumes energy, and cumulative energy consumption is a chronic problem of mechanical watchmaking.